Pneumocystis carinii is an opportunistic fungal pathogen that causes pneumonia (P. carinii pneumonia; PCP) in the immunocompromised host. PCP, as well as other opportunistic infections, underwent a dramatic rise in prevalence with the onset of the AIDS epidemic (Morris et al., “Update on the Epidemiology and Transmission of Pneumocystis carinii,” Microbes Infect. 4:95-103 (2002)). With the development of highly effective anti-retroviral therapy, the prevalence of PCP in AIDS patients has declined, though it remains the most commonly diagnosed serious opportunistic infection in AIDS patients (Stringer et al., “Molecular Biology and Epidemiology of Pneumocystis carinii Infection in AIDS,” Aids 10:561-571 (1996)). PCP is also prevalent in persons undergoing chemotherapy or other immunosuppressive therapy for cancer and organ transplantations (Morris et al., “Update on the Epidemiology and Transmission of Pneumocystis carinii,” Microbes Infect. 4:95-103 (2002)). The most common drug treatments for P. carinii infections are trimethoprim-sulfamethoxazole and aerosolized pentamidine. Because adverse side effects, recurrent infections, and poor compliance are problems with these drugs, alternative treatments or preventative measures against PCP are needed to eradicate this serious opportunistic infection.
P. carinii cannot be continuously cultured outside of its host. P. carinii also has a host species-dependent specificity which complicates the ability to use animal derived organisms to immunize humans. P. carinii organisms derived from different hosts have isoform variants of common antigens resulting in different (i.e., non-crossreactive) antigenic determinants (Gigliotti et al., “Antigenic Characterization of Pneumocystis carinii,” Semin. Respir. Infect. 13:313-322 (1998); Gigliotti et al., “Further Evidence of Host Species-Specific Variation in Antigens of Pneumocystis carinii Using the Polymerase Chain Reaction,” J. Infect. Dis. 168:191-194 (1993)). Attempts to infect laboratory animals with P. carinii isolated from heterologous mammalian species have met with little to no success (Aliouat et al., “Pneumocystis Cross Infection Experiments Using SCID Mice and Nude Rats as Recipient Host, Showed Strong Host-Species Specificity,” J. Eukaryot. Microbiol. 41:71S (1994); Atzori et al., “P. carinii Host Specificity: Attempt of Cross Infections With Human Derived Strains in Rats,” J. Eukaryot. Microbiol. 46:112S (1999); Gigliotti et al., “Pneumocystis carinii Host Origin Defines the Antibody Specificity and Protective Response Induced by Immunization,” J. Infect. Dis. 176:1322-1326 (1997)). However, immunocompetent mice immunized with whole mouse P. carinii are protected from developing PCP after T cell depletion and subsequent challenge, whereas unimmunized cohorts are not protected (Harmsen et al., “Active Immunity to Pneumocystis carinii Reinfection in T-cell-depleted Mice,” Infect. Immun. 63:2391-2395 (1995)).
The surface glycoprotein gpA is an abundant and immunodominant antigen of P. carinii (Graves et al., “Development and Characterization of Monoclonal Antibodies to Pneumocystis carinii,” Infect. Immun. 51:125-133 (1986)), although immunization with this antigen does not adequately protect against infection in a mouse model of PCP (Gigliotti et al., “Immunization with Pneumocystis carinii gpA is Immunogenic But Not Protective in a Mouse Model of P. carinii Pneumonia,” Infect. Immun. 66:3179-3182 (1998)). The majority of monoclonal antibodies (mAb) against P. carinii surface antigens react with only isoforms showing host species-specificity identical to that of the immunogen (Gigliotti et al., “Pneumocystis carinii Host Origin Defines the Antibody Specificity and Protective Response Induced by Immunization,” J. Infect. Dis. 176:1322-1326 (1997)). MAb 4F11 was obtained by selective screening of anti-mouse P. carinii hybridomas for recognition of P. carinii antigens other than gpA (Lee et al., “Molecular Characterization of KEX1, a Kexin-Like Protease in Mouse Pneumocystis carinii,” Gene 242:141-150 (2000)). MAb 4F11 confers passive prophylaxis against development of PCP when administered intranasally to SCID mice (Gigliotti et al., “Passive Intranasal Monoclonal Antibody Prophylaxis Against Murine Pneumocystis carinii Pneumonia,” Infect. Immun. 70:1069-1074 (2002)). Furthermore, mAb 4F11 recognizes surface antigens of P. carinii derived from different hosts, including humans. A screen of a P. carinii cDNA expression library using mAb 4F11 revealed a number of positive clones, including mouse P. carinii Kex1 (Lee et al., “Molecular Characterization of KEX1, a Kexin-Like Protease in Mouse Pneumocystis carinii,” Gene 242:141-150 (2000)). Based on sequence homology to its ortholog in Saccharomyces cerevisiae, Kex1 is a member of the kexin family of subtilisin-like proteases (Lee et al., “Molecular Characterization of KEX1, a Kexin-Like Protease in Mouse Pneumocystis carinii,” Gene 242:141-150 (2000)).
It would be desirable to identify a linear or conformational epitope that is recognized by mAb 4F11, which would then allow the development of passive and active vaccines for treating or preventing Pneumocystis infection.
The present invention is directed to overcoming these and other deficiencies in the art.